Determination of Safe Excavation Pressure During Hoe Ramming Activities

Abstract Hoe-ramming is a form of rock excavation, often used when an excavation area is too large for a jackhammer, or where blasting is not possible. A percussion hammer fitted to an excavator is used to break up and remove rock from the area surrounding a pipeline. During integrity excavations, hoe ramming is typically used to remove rock around in-service natural gas pipelines to allow for access to complete integrity assessment activities. To determine safe operating pressure of the pipeline, currently, a conservative approach is used that usually yields significant pressure reduction that may be unnecessarily required. Reductions in operating pressure to achieve safe excavation pressure can have impacts to typical pipeline operation. Opportunity exists to gain a greater understanding of the loading on the pipeline to allow for a more accurate safe excavation pressure recommendation. In this study, a full-scale testing and dynamic finite element analysis (FEA) were used to quantify the effects of hoe ramming activities to natural gas pipelines. Testing was completed in December 2022 at the Pipeline Research Council International’s (PRCI) Technology Development Center in Houston, Texas. The test included NPS 24 × 6.35mm NWT, Grade 359 test pipe. Some of the variables controlled during the testing were proximity of hoe ramming to the test pipe, internal pressure (hydro) of test pipe, and configuration of the granite block and test pipe. Two configurations of granite blocks were subject to hoe ramming while in contact with the pipe were tested: including, I) Test pipe on top of two granite blocks, and ii) test pipe on side of one granite block. Accelerometers and strain gauges were instrumented on both granite blocks and the test pipe. Temperature, test pipe acceleration, test pipe strain, and internal pressure data were collected while the granite blocks were subject to hoe ramming. The data was processed and analyzed to quantify the effects to the test pipe during hoe ramming effects on the pipe. When reviewing stress levels because of hoe ramming, both testing and the dynamic FEA supported that there was no detrimental effect to the test pipe. Further dependencies such as proximity of hoe ramming to the pipeline and internal pressure were also investigated. The test results were used to validate the FEA model of the tested configurations, which can subsequently expand to parametrical models to cover additional scenarios and understand the influence of critical variables. Outcomes of this study include development a pressure-equivalent method to determine safe operating pressure during hoe ramming activities. Details of the testing and assessment are summarized in this paper.